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What happens if a student busts Dallas Fort Worth bravo airspace?
What would happen if a student busts a corner, exceeds the floor of Bravo airspace by 500 feet then descends after one minute?
The pilot is on the frequency of a Golf airport heading towards a Delta controlled airspace, both within the Bravo 30 nm veil.
Does the Bravo tower have a way of knowing the aircraft involved?

If they are squawking VFR they probably won't know who it was. Either way I'd file an ASRS report detailing the incident. If they do know who it is, the flight instructor will probably get a talking to, and to a lesser extent, the student pilot.

Just to make it perfectly clear:
If you accidentally enter a controlled airspace without clearance, as soon as you realise what has happened, the first thing you do is contact the responsible ATC unit! Period.
Panicking, initiating a rapid descend to leave the airspace or simply pretending it didn't happen is extremely bad airmanship, and will surely get you in trouble if you get caught. On the other hand, admitting you made an honest mistake and asking ATC what the best solution is might still get you in trouble in some countries, but it is definitely the safest solution for everyone.
Depending on the exact details of the airspace infringement, it may be extremely dangerous if you try to solve the problem on your own. By suddenly descending to leave the airspace, you risk colliding with traffic below you. If the airspace in question is of a military kind, turning a blind eye to your mistake and maintaining radio silence will potentially result in a visit from some aircraft with a lot more weapons than yours.
Anyone can get lost and make mistakes. If you do, ATC is there to help you - not to punish you for an honest mistake. Make use of that help!
As for procedures about which forms need to be filed after an incident like this, I will leave it to someone with knowledge about FAA specific procedures to answer.
You can read more about Airspace Infringements at SKYbrary.

Well, it depends.  Controlled traffic around these satellite airports would be on the Class Bravo's approach frequency.  If you were in that category and contacted approach and they had given you flight following or assigned a transponder code to you, then yes, they would know it was you and be able to track your aircraft down, if they were so inclined to investigate.  Also if you were in contact with the tower at the class D airport and they had previously located you, then it's possible you could be notified about that.
Yes, theoretically you could get in trouble for that.
Now uncontrolled traffic squaking VFR would be more difficult to identify.  ATC may note the radar return which violated the controlled airspace and track it to its destination, but further pursuit would probably be wasted effort.
If you did this, just make a mental note of what happened, what caused it, and vow not to go down that path again.  Most likely nothing will come out of this.  Save for major, intentional tresspass of these types of controlled airspace or violations which result in an incident or accident, the authorities will just note that it occurred and won't wast the time or effort on further investigation.
TFRs are another story altogether.  Violate those and you can expect an airborne visit from a couple of nice young men flying F-16s who will have instructions to follow them and land at a nearby airport.  Police will most Likely arrest you there.  Expect to spend the day chatting with a couple of nice people from Homeland Security before being released and receive a letter from the FAA informing you that they are revoking your pilot's license.

I didn't downvote, but "receive a letter from the FAA informing you that they are revoking your pilot's license" is not at all accurate. The FAA very very rarely takes so much action as to revoke your license in almost any circumstance. Usually what happens is a temporary suspension. If you bust a TFR you are not automatically escorted, usually the controlling facility will contact you and ask for your information, after which an investigation will be launched. The only time you get a fighter escort is if you were to ignore or not comply with any instructions.


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What are the differences between PNL and PNR messages?
What are the differences between Passenger Name List (PNL) and Passenger Name Record (PNR) message in CRS systems?

source: Stack Exchange

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in non precision approach, why use 2 NM before the final approach fix to start the landing configuration?

i know when vectoring aircraft to the final approach course,controllers are required to ensure the intercept is at least 2 NM outside the approach gate and there is a raim test at 2nm before faf but obvisouly that is not the proper reason.
and for circling approach, i know some company use 2nm before faf to get flap20(boeing) confirguartion to continue the approach(for circling approach fctm and fcom just mention at mda to make landing confirguartion), which one is the right procedure?

some airports faf is just 4nm, eg ymml rnp34, i think it is not suitable to start making landing configuartion at 4+2=6nm, so why boeing use 2nm before faf in sop?

I believe the main reason behind this SOP is to set the DA/MDA and verify modes before the FAF. Re. Allowing for good workload management. I will probably write a longer answer in due course.

As a minor correction, Approach isn't required to get you intercepting the approach course outside 2NM from the gate, that's simply best practice. It's permissible to vector someone closer than that but the maxima are tightened at that point (i.e. the size of the turn to final course goes down from 30 degree maximum to 20 degrees to allow the turn to happen in the shorter distance).  Even vectoring inside the gate is permitted - but the pilot has to specifically request that.  Meteorological minima also apply inside 2NM of the gate.

The approach YMML RNP Rwy 34 has two minima lines and you use the top graphic for the LNAV approach and the second precision approach graphic for the LNVAV/VNAV approach.
These procedures are developed to allow you to slow down and configure without adjusting thrust on the engines.
Let me answer your LNAV question.  You want to be stabilized, fully configured and on speed (VREF) when you decide to descend to the MDA.
For this approach, will will cross AKDEL with flaps 5 and a specific speed.
once you cross AKDEL you are cleared to descend to 1,500 FT MSL at the speed recommended for the airplane you are flying.
If you are at the correct speed and you level off, you will add power necessary to maintain that speed.  At 2NM, you will configure flaps 20 and gear down.  You shouldn't need to touch power as the extra drag will slow you down.  If you planned it correctly, you will be on the correct VREF speed at the FAF where you add full flaps and start to descend.  Again, very little thrust lever movement should occur to stay on VREF while descending down to MDA.

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What are the requirements for a foreigner to become an Air Traffic Controller in Sweden?
Background
I am an Air Traffic Controller (ATCo) working in Greece and I'm looking for information about working in Sweden as a foreign ATCO. I speak Swedish and my wife is of Swedish origin (not a citizen though).
My question is...
Is it possible for foreigners who know the Swedish language to get a job in ATC in Sweden? Where can I find vacancies for ATCO positions in Sweden?

@Stelios Adamantidis.I have created the account in order to get answers and to give,if i can.Ive been visiting AVIATION for a long time,before i decide to join.

@fkoris I've seen your profile when you first created it and was marked as unregistered, no hard feelings. :) And welcome to Aviation SE. -Note:Previous comments removed

Sweden currently has a surplus of controllers, so you are unlikely to find open positions. However, since you are a qualified controller and speak Swedish, you should be qualified to apply for any position that might come up. I suggest you have a look at LFV, which is the largest Swedish ANSP: www.lfv.se/en

So,there is no nationality-citizenship restrictions for hiring an atc?Are there any openings that might come up in a long term period?My objective is to have succeded working in Sweden  within the next 3-4 years...Thank you for your time and your help..

Remember that Sweden and Greece are both EU-countries. Nationality based restrictions can be based on "EU-nationals only", but "our country only, no nationals from other EU countries" is illegal in most cases. So in theory there should be no restrictions. Whether or not this is the same in practice can only be answered by an insider, who probably won't admit any bias for legal reasons.

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When and how is CPDLC established?
On a typical commercial trans-Atlantic flight, say from Frankfurt (EDDF) to New York Kennedy (KJFK), on a typical airliner (B777, A380, B787, etc.), when are Controller–Pilot Data Link Communications CPDLC established?

Is it generally before take-off, or just during the flight?
Is it only used during oceanic crossings, or for continental flights, too?
Will ATC instruct the pilot when to use CPDLC and when to revert back to voice communications?

Using CPDLC makes life easier for pilots so we typically use it whenever it is available and logon shortly after takeoff.
When departing Frankfurt there is no rush as CPDLC is not available until crossing into Maastricht Radar. Continental USA does not have it so you lose CPDLC after Moncton Center.
ATC will often remind you, or ask you to logon if you have forgot as it makes life easier for them too. Where VHF is available we usually use a combination of voice and CPDLC.
Over the ocean, out of VHF range, we have to establish HF radio contact with Shanwick or Gander radio and do a Selcal check to insure we have a backup communication method.


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What would happen to the aircraft and its control surfaces immediately after the loss of all hydraulics?
In cases like the DHL shoot-down in 2003 or the Sioux City crash, both aircraft lost all of their hydraulics because of a catastrophic failure of aircraft structure.

What would happen if the aircraft just suddenly lost hydraulic power mid-flight?
Would the flap goes flat, or would in droop down, increasing lift, and force the aircraft into a phugoid motion?

I am talking about the same aircraft types presented in these disasters (big civilian transports) like Boeing 747-400.

See this Airbus analysis of the Baghdad shoot-down incident.

This might help in understanding what could happen.

Assuming some sort of catastrophic failure of all three or more hydraulic systems in flight, and no emergency hydraulic power, it would all be based on the design of the systems on the specific aircraft, but, most likely, the following would happen:
Flaps would remain in their current configuration. Flaps are driven by screw drives with your powered from a torque tube driven by a hydraulic motor.  This would not move position as a result of a hydraulic failure.
Landing gear will remain retracted. Large airliners have an uplock system, which holds  the gear in the retracted position during flight.  If the landing gear were down and locked prior to the hydraulic failure, they would remain down and locked afterwards.  The downlocks are held in an over center position by spring bungees which require hydraulic pressure to release.
Flight controls would not function, nor could they be commanded into positions by the pilot, unless there was a mechanical backup of some sort.
Other secondary flight control systems, such as spoilers or speed brakes also could not be deployed due to the failed hydraulic systems.
Keep in mind, the sort of a scenario would be virtually impossible as there are multiple redundant failsafes on these systems.

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Propeller Torque
We know that every rotating device generates torque . How does a single engine propeller A/C (Piper) counter-balance the torque which is being produced by nose propeller?

Using the ailerons on the wings.
The torque is a roll moment and the ailerons will be able to counteract that easily.


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What do you do when your engine quits right when the airplane starts off the ground?
This has been one of my fears in flying (a plane the size of Cessna 152). I sort of know what to do when the engine quits on you when you are a few hundred feet off the ground, although it is definitely not easy to manage. However, lets say you are just past the rotation speed and have very little runway left. Is there anything you can really do other than cut power, retract flaps and try not to set your brakes on fire?
Edit: I am assuming that I am barely 10 feet above the runway. I suppose this is a more specific version of the general case of engine failure at lift-off.

@Federico I don't think that question is a dupe, it's about losing one engine in a twin-engine aircraft. This question seems to be about losing engine power completely immediately at very low altitude.

@Pondlife point taken. VTC retracted

This is a duplicate

@Federico To be fair, I didn't realize that either until I read the other question more closely. I've edited it now to make the multi-engine point more obvious.

The first and perhaps most important thing to do is NOT turn around. Generally speaking you won't have the airspeed/altitude to make a full 180 and return to the field. While it can be done, it's advised to continue forward and put the plane down as you would in any emergency. Trim for best glide and pick a landing spot (limited options in this case).
In some cases with small plane/long runway situations you will be able to execute something like a short field landing with the remaining runway but that is very situationally dependent. When I flew out of KPNE in a Warrior 24 was 7000ft; if you lost an engine at rotation you had plenty of runway. At DYL where I fly now that's not really the case. Every airport is different but a good deal of the airports I have flown out of recently have had long fields at either end of the runway giving maybe an extra 1000 ft or so. Airports in populated areas may have roads you can touch down on.
You should always consult the POH of the specific aircraft in this case for proper emergency procedures.
Specifically to the 152 point, the take off distance is around 1400 ft. full loaded if memory serves. Unless you are training on 2000 ft strips you should have no problem getting the plane back down with remaining runway at all but the shortest of fields. If you are only 10ft up you should be able to put the plane down fast, albeit a bit hard, but fast none the less. For what it's worth Cessna landing gear can take quite a beating. Once you have touched down it would be advised to retract your flaps, this will increase the load on the gear (by reducing your wings' effectiveness) and increase brake effectiveness. You should take care to not lock the brakes as well.
Side Story: This happened to a buddy of mine in his Archer a bunch of years back (I'll try to find the incident report). The plane was fresh out of annual and something was not hooked up correctly and shook loose on take off causing the engine to cut out around 100ft or so. There was a corn field dead ahead and he was able to put the plane down smoothly. Thankfully no one was hurt and he simply owed the farmer for the corn he took out on landing….

I will an instructor if I can safely train for this somewhere. It would be good to know that I can do it instead of needing a change of trousers. I am thinking KSTC. They have enough runway to land small regional jets.

You will eventually get to the point in your training where you are doing short field landings its required for the PPL PTS.

I know how to do short field landings. So, I guess that counts. I already have my license but I will still keep practicing.

@NullReference: Anecdote for you. I did my private pilot training at KEAU in a C152. Once, my instructor had me to a touch and go landing and then pulled the throttle out shortly after we lifted off. I simply landed on the remaining runway. Not that big of a deal with a 7300' runway. I don't think it'd be any harder at KSTC.

In that case you can try for a short field landing of sorts. The other option of course is to get your Multi-Engine Rating and start flying twins ;)

How much was the corn worth? :)

Corn is only worth somewhere around $750/acre. The crop damage could be the cheapest part of an incident like this.

Remember to pull the throttle if the engine fails so it can't start again just as you have settled down. I would not mess with flaps; you have too much else going on at this stage and retracting them serves little purpose.

This is where the term "bought the farm" came from.

If the engines quits right after the plane has lift off, you can easily set it back onto the runway. You will be amazed how short the distance is to stop a C152.
I would rather leave the flaps untouched and focus on where I am going, unless you are a skilled bush pilot used to playing around with the flaps. Then again, if you are a skilled bush pilot, you should have no problem landing in incredible short distances.
Of course, being a Cessna 152, chances are your runway can accommodate planes of larger size, like a Cessna Caravan, so you're likely to have some runway left. Unless you messed up your takeoff performance calculation, "just past rotation speed with very little runway left" sounds a bit remote to me. If the engine quits by the time you reach the end of the runway, you should be at least a couple hundred feet high, making a turn possible. Oh yea, make sure you experiment this turn at altitude, so you don't commit to the impossible!

Thank You. This is something to add to the list of items on my advanced training. I will try and determine how much altitude I might lose in a 180 turn at take-off speed. Most people, however, would advise against turning around. I want to know what my airplane and most importantly I can do as a pilot before I do get into such a situation.

If you're training, your instructor would recommend some values to you before you go solo. Engine-Failure-After-Takeoff should be one of the briefing items before a flight.

It does terrify me to think that that my instructor did not mention it. It is my job to ask him. So, I cannot blame him completely. I did manage to get a Private Pilot Certificate but I treat myself like a student. Enough people have warned be against letting that blue plastic card make me think I am invincible.

When I received my Private license, the examiner told me it was a "license to learn"

Mine told me something on those lines too. I taught a few friends how to drive and I tell them the same thing. That little phrase is versatile.

Never think that you're invincible.

@NullReference, the big risk in trying to turn around is stalling. To fly a tight turn, you need to fly it slow, the high bank angle (~45°) increases your stall speed and the stall warning device will sound later when it is on the outer wing, because the outer wing is slightly faster. And of course if you stall in a tight turn, you are likely to enter a spin.

+1 for not screwing with the flaps at this point unless you already feel comfortable.  Attitude and airspeed first.  Avoid the power-off stall.
To expand on the last paragraph:  as you advance, one of the skills to pick up is to know where you're going if things go wrong.  That includes when you're committed to takeoff, when you're not coming back to the runway after liftoff (this is when I raise landing gear in certain aircraft), when the best option is the cornfield, and when and where you have altitude to come back to an airport.

What's described in the last paragraph seems like a good thing to try out in a simulator as well. Sure it'll be far from a perfect rendition of reality, but mixing some flight simulator attempts with real life trials at altitude should give a decent idea of what to expect should it ever happen in real life. @NullReference


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Why is this video of a G36 Bonanza taking off so scary?
Why is this video of a G36 Bonanza so 'scary'?

If they had clipped the top of the trees, would it really have brought the plane down? (And even if yes, it looks pretty survivable).

On what basis do you think falling to the ground several hundred feet below while going 70 MPH is "survivable"?  Such a car crash would frequently be fatal, and cars have far more safety features than small planes.

I don't think those trees were "several hundred" feet tall.

Because those trees will kill them
If you look at this document regarding the Bonanza G36 performance you will note that the lowest stall speed written is 61 kts. 61 kts is 112 kph or 71 mph. We can assume they were going a little bit faster than that but let us say 110 kph / 70 mph.
In that clip, they are just barely keeping airborne. This means the aircraft is extremely sensitive to disruptions. Any loss of power — even partial — or getting knocked back by a collision and thus losing a few knots or upsetting the aerodynamics of the aircraft, is very likely to send it crashing into the trees.
Going 110 kph / 70 mph into a tree is rarely survivable even in a car, and then you have to remember that cars these days are built to withstand crashes while at least keeping the occupants alive, but that assumes crashing into something wide, that distributes the forces over a wide area, and that gives way, like another car. Trees fail that on both accounts.
A G36 does not even come close to any such structural integrity in case of a crash. The cabin will crumple like figurative tin foil, sending the occupants smashing into the trunks of the trees, or throwing them clear of the aircraft only to then smack into other trees or the ground from several meters up and at a high speed. And that is going to be fatal.
Hence, this is scary because if they clip a tree they are very likely to die.

I found out a bit more about this incident... it seems that one of the passengers wasn't honest about their weight and they had already dumped fuel to be inside the flight envelope (probably why the stall warning sounded as soon as they rotated?)... Thanks for the answer :)

The survivability of that kind of crash is basically a crap shoot.  The rear seat pax will almost certainly live if there's no post crash fire.  The front seat occupants, it will depend on the sorts of things they run into during the crash sequence and how much the front end of the cabin is deformed.  They  might get lucky, they might not.  Coniferous trees are better than deciduous trees and can be like landing in a big hair brush if they are small and dense.   Bigger ones, not so good.  If an engine quits while I'm over a forest carpet, I'm heading for small conifers if I can identify them.

@JohnK Assuming you go head on into the trees. Any "side slip" (i.e. the plane starts turning during the impact) and you have nothing but thin sheet metal / composites between you and the tree trunk coming at you at 50+ mph.

@JohnK I never knew dendrology would be useful in aviation ;)

Keep in mind that older aircraft often fall a little short of their published performance charts. Dirty wing surfaces, little chips in the prop, they all rob just a bit of lift, add a bit more drag. People lie about their weight, or you mis-estimated something. Density altitude could have increased substantially as the temperature climbs, you should always add a fudge factor!

@GdD For the sake of keeping this answer credible and free from controversy, I am going with the lowest possible speed I can. Yes, in reality they were probably closer to 120-130 kph / 77-85 mph. But I do not need that for the answer, because imagining crashing into a 9 m / 30 ft tree at 110 kph / 70 mph is a mental image that scary enough to get the point across.  :D

No but the most significant mass of the airplane, the engine, is the first thing to hit and the wings are protecting the cabin to some degree.  The cabin remains intact in the vast majority of crashes unless the plane runs into something solid before any energy is used up. If the airplane hits a wing on a trunk and starts spinning around, the wings can end up absorbing a lot of the energy, or even the tail if it spins around and hits the ground backwards.  You're going to be hurt, but most crashes are survivable if the front seaters are wearing shoulder harness and there is no post crash fire.

@JohnK Well now we are not talking "most crashes", now we are talking about a very specific set of circumstances: small general aviation aircraft, going into a dense forest of sturdy 30+ ft conifer trees. It is not like a big airliner going down on a smooth desert floor. :)

I was not criticizing your good answer @MichaelK. What I mean is that the pilot got in that position by not taking it into account, among other things.

Maybe maybe not. Lots of people survive crashes into trees, especially coniferous ones which absorb the energy very well.   https://www.youtube.com/watch?v=OVM3RRd1vf0.  The only crashes with the guaranteed probability of death that you are implying are when airplanes go straight into the ground; ie, stall spin or similar.   A controlled descent into coniferous trees, maybe, maybe not.

I think the verbiage is pretty important here. If they "clipped" a tree, they should be fine. The amount of momentum they have at that point is pretty great, and treetops are quite elastic.This wasn't a case of narrowly avoiding treetops and barely escaping certain death, this was a case of narrowly avoiding atmospheric conditions that, if any worse, would have had them running into more trees and thicker areas. At 1:45, he says "Wow!", and there is a treetop to the left, that treetop would not have been enough to bring them down. This isn't aviation experience talking, this is physics.

@BluegillPrime Ingest a branch into the propeller, buckle a leading edge, cause a startle that makes the pilot make a maneuver... anything at that point may eat up the last little margin they have.

That's true. I was speaking more to clipping the wing or gear. An evergreen at that height would not buckle a leading edge.

anyway, many so called "try not to laugh" videos on youtube are very close to fatal, yet they do not look scary; this also may be close to fatal by it's not scary at all

I know it's been a while since this was posted, but I'm the pilot flying this aircraft. Some interesting assertions are made here throughout the comments.
Some facts:

We were about half fuel
3 guys, roughly 180 pounds average weight
Turbo Normalized
Roughly 70º, Decent headwind on takeoff

Steve Thorne (FlightChops) makes this about Density Altitude, which is not accurate.
My opinion after having been through it, reliving it many times, and reviewing the video, was mechanical turbulence. There was a river down and too the left, and a 'hill' above that. The trees are pretty solid on the first half of the runway, channeling the wind down the first half of the runway just fine.
The remaining half, I believe two things happened: A headwind sheared to a crosswind at the time of rotation and B the mechanical turbulence was down-washing onto the runway essentially holding us down.
Basically we lost much of our critical flying speed at the wrong moment.
To make matters worse, in the post mortem, I learned that the takeoff technique in the newer Bonanza manuals had been changed because of fear of liability by Beechcraft. There are much better procedures that can be used (flaps 20, or full flaps and keep the gear down) that would have made this a non-event.
Perhaps one of the biggest lessons I've learned is not to trust the FAA or any flight school as the be-all-end-all. There are many different ways to look at a situation, evaluate a landing location, and more holistically view a procedure than simply the "FAA Way". That's what I did, and it almost got me killed.
Also, I hope this isn't about my takeoff, because it's pure fiction:

I found out a bit more about this incident... it seems that one of the passengers wasn't honest about their weight and they had already dumped fuel to be inside the flight envelope (probably why the stall warning sounded as soon as they rotated?)... Thanks for the answer :)

What would be the advantage of keeping the gear down?  Is extra drag created during the retraction cycle?

Likewise-- would full flaps really have been optimal?

Full flaps presumably gives a lower stall speed. Gear up with full flaps probably gives a warning horn, so gear would remain down until after initial flap retraction.

Thanks for coming by to address this. And thanks for being honest enough to set yourself up for the potential for abuse over it, too. Admitting mistakes is never fun or easy, but it's the best way for others to learn how to not make them.

Hi Chris are you the author of "angle of attack"?

@RalphJ - you would accept extra drag just to keep a horn from sounding?  In a tight situation like this?

@quietflyer  As a standard procedure, you'd do things in a way that keeps warning horns silent. At the point where things get ugly, yeah, you might consider retracting the gear & living with the horn.

They Trimmed the Margins to Zero
In this video, the aircraft takes off and flies a straight course through the trees and continues a shallow climb out.  To the uninitiated, this may appear innocuous, until one realizes that the aircraft was performing at it's maximum limits with near zero room for error.
The voice and narration of this video does a good job breaking down what happened in this scenario, to recap in writing:
The pilots appear to have calculated the takeoff performance, found it to be adequate and made their attempt.  Their calculations were likely correct, but sufficiently lacking in margin so as to excite those on board who were cognizant of the situation.
It is reasonable to assume that aircraft performance tables are generated under near ideal and non-threatening conditions.
It is also reasonble to assume that:

A pilot who flies recreationally may not be able to squeeze every bit of rated performance out of their aircraft.
Mistakes can be made in the calculation of weight and balance which affect performance.
Conditions may change between the time calculations are made and time of takeoff.

Near the end of the commentary, the pilots can be heard verbalizing their learning experience.  I think the lessons of the experience are not lost on them.
Lessons of aircraft performance are somewhat frightening to me as an aspiring instructor.  Training usually occurs at one airport, often with a long runway, with one aircraft or type of aircraft and one loading scenario.  If the training is compressed into a few months, the student may not even be exposed to a significant range of weather conditions.
I intend to teach my students to be awake to the amount of runway they are using and load the aircraft in multiple configurations as part of the training.  I think many pilots have a moment of nervous surprise the first time they experience narrowing margins.  I would like it to be less of a surprise.
Learn from this video, and from this other one, which had a less fortunate ending:

As long and explanatory as this post is, it still does not answer the question: why is this (considered) scary. You are explaining how they go into the situation — and admirably so — but the question was not that, but why the situation is considered scary.

What was the cause of the crash in the video you posted? Was he intentionally flying low like that?

@MichaelK To me, the human behavior of failing to provide margin is a hazardous, and potentially mortal error.  That someone would entertain an attempt an operation on the grounds of a calculation with zero factor of safety frightening not only on account of the operation, but that they may have developed a habit of doing so.

@Cloud, very doubtful that the low flight was on purpose.  The NTSB report cites a failure of the pilot to account for air density (density altiude), which is a factor in figuring takeoff performance.  The air density was simply too thin for the aircraft to climb with the load it had.  Additional scariness comes from how poorly this facet pf performance is understood and applied among pilots.  https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20120701X65804&AKey=1&RType=HTML&IType=LA

Said another way, this video is scary because is represents an unfortunately too common occurrence of pilots being unfamiliar with performance limitations, or failing to recognize when they are near the edge of their aircraft's capability.  This may merit another answer on it's own.  So, @MichaelK, we have at least three reasons: 1. Trees will kill you, 2. These Pilots made a mistake (which they are less likely to repeat after this experience), 3. Too few pilots realize this problem and may have to learn it on their own, endangering theirs and others lives.

It seems to me that in the video in the question, the pilot might have had some margin for error, but cut into it by flying slower than best angle of climb speed. While they managed not to stall the aircraft when approaching the trees, the stall warning on rotation and then again during climb-out suggests they rotated too early and tried to climb very slowly instead of accelerating to $V_x$ in ground effect as the usual short-field technique calls for.

What makes it scary is just how close they did come to an accident.  They attempted a takeoff using the performance calculations listed in the POH on a hot day at high field elevation.  That’s fine assuming EVERYTHING works out just like the book ie no errors in calculating performance, aircraft and engine in peak condition, field atmospherics, perfect short field takeoff technique, etc.  But as the video showed, they came damned close to clipping the tree tops on climbout.
The aircraft in question was a turbonormalized G36 departing from Mears Airport (3W5) in Concrete, Washington.  The small country airport is located in a river valley surrounded by mountains. According to the pilot the performance calculations show that the aircraft could do it, and so he attempted to try it. Fortunately he managed to weave his way through the trees at just under stall speed to get clear of obstacles and clean up and accelerate the aircraft out of the reverse side of the power curve.  The film is scary because it shows just how close he came to having a controlled flight into terrain or striking obstacles.  Mountainous terrain quite often has downdrafts coming through the valleys on the windward side. Had he encountered one, he would have never made it.
The airport is built on a small flat land surrounded by rough terrain. Had a pilot collided with the treestops at the end of the runway, there was a good chance that he would have lost control and crashed.  The likelihood of survival in a situation like that, particularly in a high-performance airplane like a bonanza climbing out at 80+ knots, is not great.


text:
Would a tumbleweed sucked into a jet engine on takeoff cause a serious problem?
I saw tumbleweeds going across flight path in El Paso, TX and it made me wonder, especially after seeing what birds can do.
Would a tumbleweed ingested by a jet engine on takeoff cause serious problems?

To the tumbleweed? Then yes. (sorry, I couldn't resist..., but I like your question ;-))

It's not uncommon for some vegetative material to be sucked into engines. Most civil jet engines are high-bypass engines so the great majority of the air (and anything in it) goes through the fan rather than the engine core. If you look at the fan of an engine that's been in service for awhile, you'll see nicks (most of them dressed out hopefully) from harder material that's gone through them. My guess (emphasis on  guess) is that a large engine could take a small tumbleweed without serious problems, but lowering that ratio would increase the probability of trouble.

@PerlDuck: Given that a tumbleweed is already dead when it tumbles, serving merely as a seed-dispersion mechanism, being sucked into a jet engine might actually be very good for it, given that (assuming most of it goes through the bypass duct, which it probably will) the tumbleweed would be disintegrated and its fragments scattered far and wide by the jet blast! :-P


text:
In parallel runway ops, is it better to dedicate a single runway to landings, or is it best to have a mix?
Assuming taxiing is not a consideration, in an airport with two parallel runways does the airport gain capacity by:

having a single runway dedicated for landings and the other for take-offs, or
is it best to have both take-offs and landings from both runways?

Would there be other ways to divide the movements (say by class/size of aircraft)?

There are a number of things to take into account:

The distance between the runways; can they be operated as independent runways? This requires the centrelines to be more than 1035 meter apart.
The traffic mix: is there constantly the same distance between landings or a large gap every now and then between a Heavy and a Medium that allows for one or two departures in between?
The runway entry and exit points. Can aircraft wait sufficiently short of the approach end to allow for a rapid departure when cleared for take-off? Does the runway have high-speed exit taxi-ways at appropriate places for the landing traffic to vacate the runway quickly or is a slow 90 degree turn required?

In general, mixed mode operations can increase capacity significantly. For example the estimate for London Heathrow is that the traffic could increase from 480.000 to 540.000 movements.
But it is not a simple change. The requirements on ATC increase. For example, to monitor the parallel approaches, the update rate and accuracy of the surveillance system must meet higher standards than for single runway approaches. Also missed approach and emergency procedures need to be changed.
And then there is an important noise issue; in mixed mode operations, all four runway ends are continuously exposed to aircraft noise, while in dedicated operations the departure end of one runway and the arrival end of the other is not exposed.

"Back of the envelope" estimation:
For simplicity let's assume traffic that is only Medium wake category with 3NM final approach separation at about 150 knots groundspeed. This would result in ~75 seconds intervals between aircraft passing the threshold for a pure landing runway, allowing for 48 landing per hour.
In mixed mode, a line up and hold instruction would be given as soon as the landing aircraft is passed the numbers, so take-off will commence quickly after take-off clearance is given. The take-off clearance itself can be given as soon as the landing aircraft has vacated the runway, which should be about 60 seconds after it crossed the threshold. The take-off run itself is 30-40 seconds for B737 / A320 family aircraft. Let's add about 20 seconds reaction and engine spool up time + margin. The next landing aircraft can cross the threshold after lift-off. The interval would be ~ 120 seconds between landing aircraft, resulting in 30 landings per hour. But this can be done on two runways at the same time, effectively increasing the throughput by about 25% percent.
The above schedule is very idealised with pure alternating take-off and landings and little margin for error. If put in practice it will probably result in too many go arounds due to late take-offs, but it gives good idea of the capacity increase that is possible.

Your link is exactly the kind of research I'm after. It seems it's an open question but that the evidence leans towards mixed-use operations. This is surprising -- thanks!

That would no doubt depend on a lot of factors. Geometry for example. If the parallels are far enough apart there's no chance of a missed approach on one interfering with traffic on the other, you're a lot more flexible than when they're close together.
Maybe you have noise abatement procedures that make the use of one of the runways for either landing or departures illegal at specific times (e.g. Schiphol can't use certain approaches during the morning rush because overflight of parts of the city are not allowed at those times).
Type of traffic is another. If you're getting a lot of inbound heavies at an hour where you have a lot of outgoing smaller aircraft, it soon becomes a good idea to have one runway set aside during that period for landings, one for arrivals (the wake turbulence of the heavies would mean longer waiting times on the runway for the lighter aircraft).
So overall, there's no definite answer. It all depends on traffic, local conditions, etc. etc.


text:
How do planes respond aerodynamically when bringing them into inverted flight by rolling?
For the sake of the question the plane is fully capable of inverted
flight, no problems with engines etc.
Background of the question is the observation that the airflow around
the wing must also invert the direction. If I look from the end of the right wing in direction of the fuselage, I see the air moving around the wing counterclockwise, while inverted it must spin clockwise. So at one point the relative air flow must cease completely on average, there is no difference anymore between top and bottom of the wing.
While the airflow is not turbulent, this should feel for the pilot like stalling because there is no lift, also the wingtip vortices should stop. The "no lift" position should be somewhere near the point when the plane has its wings vertical.
So once a pilot brings a plane into a roll, what exactly happens? Is it a smooth transition from full lift to no lift to full lift back or is there a sudden loss of lift which must be overcome by spin inertia? I have also the suspicion that trying a roll with a too high angle of attack risks a real stall because the restart of the circulation around the wing is hampered.

I fly such a plane.  My Laser has full inverted systems (oil, gas) and symmetrical airfoils.
You're right that when in upright flight the wings are producing lift in the direction away from the wheels and when in inverted flight the lift vector points in the opposite direction.
You're also correct that the wings are producing zero lift at 90 degrees of bank.
As for what happens during the roll, there's a smooth transition.  Assuming you're maintaining a constant heading, the lift provided by the wings will decrease to zero by the 90 degree of bank point, then resume in full at 180 degrees of bank in the opposite direction relative to the wing.  As lift decreases, the nose of the aircraft will typically decrease precipitously.  It's not an aerodynamic stall and there's no sudden onset.  It's just like rolling into a diving turn with the turn.
This is why trying to roll an airplane with no previous aerobatic training can be fatal.  That "simple roll" you tried can easily result in a >Vne dive.
There are 3 ways to not lose altitude during the roll:

As you suggested, roll fast enough.  My plane will roll a full 360 degrees in a bit over 1 second.  There's not much time to lose altitude :-)
Use "top rudder" (the foot closest to the sky) to lift the nose up.  At the 90 degree point you're using the side of the fuselage as a crude wing.  It works in the right airplane.  It requires an unusually large rudder and a lot of practice.
Anticipate the loss by pitching up a LOT before rolling.  You'll get more of a barrel roll, but it's still a roll.

Please don't try this without competent training.  Stupid people die this way.

I've always wondered what an airplane with spoilers only for roll control, like a Northrop Black Widow or Mitsubishi MU-2, would do if you were slow rolling it and got to the inverted flight part.  Would the extended spoiler, now on the "bottom" of the wing, act like a split flap and help with negative lift and continue the roll? Or would the opposite happen?  Or some kind of in-between effect?

Sage advice.  Thanks.

@JohnK - You should post that as a new question - I have no idea.

Thank you very much. I am no pilot, I was simply interested what the reverse flow does for a pilot from the viewpoint of a scientist. :)

@ThorstenS. You may also be interested to try and figure out what happens when the wings are 90 degrees in situation 2. Certain stunt planes can not only fly inverted but pause in the middle of the roll and fly with their wings vertical. This is called "knife-edge" flight. Hint: the rudder thing mentioned in situation 2 is basically the pilot using the rudder as an elevator.

@qq jkztd  not so sure about that.  Maybe it depends. If a spoileron is just ahead of the flap and is extended say 20 deg in inverted flight it may produce an upward lift increase as if it was a split flap.  I'd like to see some actual test data.

"Stupid people die this way." +1 for that alone!

"... the wings are producing zero lift at 90 degrees of bank."  As long as there is positive G and positive AOA the wings will produce lift.  At 90 degrees AOB your lift vector will just be parallel to the horizon.  More correct would be to say that the vertical component of lift the wings are producing is zero.  (hence the need to produce lift with the fuselage if you intend to hold altitude...)

If I look from the end of the right wing in direction of the fuselage, I see the air moving around the wing counterclockwise, while inverted it must spin clockwise.

Note you could do the same thing simply by putting the aircraft into a dive.  All you need is for the angle of attack to be negative.  As it passes through zero angle of attack, the lift falls to zero.
While lift goes to zero, air is still moving over the surfaces.  So as long as you stay away from stalling, it remains controllable.

"If I look from the end of the right wing in direction of the fuselage, I see the air moving around the wing counterclockwise, while inverted it must spin clockwise, while inverted it must spin clockwise."  What does this even mean?  The air flows from the leading edge to the trailing edge along the top and the bottom of the wing, not clockwise or counterclockwise.  Rolling inverted, whether maintaining +1, zero, or -1 G does nothing to change the direction of the flow over the wing.

@MichaelHall, see http://large.stanford.edu/courses/2007/ph210/glownia2/  or https://www.spsnational.org/sites/default/files/files/publications/observer/2015/elegant-connections-physics-lift-circulation.pdf.  The circulation is a result of the lift.  In inverted flight (or a steep dive), the angle of attack is negative, and the circulation is reversed.

OK, so there is a pressure gradient component here that I think is misleading.  I haven't fully digested what the authors are trying to convey, but Neuenschwander's figure 5, and Laughlin's figure 4 can be misleading.  Air does not flow circularly around a wing, it flows from the leading edge to the trailing edge.  Just like the other figures depict.  Just like you would see it in a wind tunnel.  Also, any discussion of "inverted" flight should caveat whether it is sustained negative 1G or not.  Because a roll can be made while maintaining positive Gs and AOA.

If you are positively loaded all the way around the barrel roll, the circulation around the airfoil never stops, the plane just brings the circulation along with it.  Like if you had an airfoil section making lift in a wind tunnel and you rotated the entire tunnel through 360 degrees of rotation.
On the other hand if you "push" to shift into negative-loaded flight as you approach inverted then yes, there must indeed be a reversal of the direction of circulation around the airfoil.


text:
What are the performance adjustments for a Beechcraft B1900D on a wet runway?
I am doing runway analysis for B1900D and AFM Section 5, does not provide correction to V1 or the takeoff weight for takeoff on a wet runway.
Appreciate if someone can provide information regarding such correction or the method.


text:
Why is the forward fairing of the pylon very shiny and metallic in appearance in A350?
One can notice the forward fairing of pylon is very shiny and metallic. This is quite unique and I do not find it in other aircraft. Why is this?
Does it serve any specific aerodynamic purpose or does it house any anti-icing provisions?

I don't really know the answer but if you note, all the other "leading edge" surfaces on the A350 are unpainted.  That part appears to be a leading edge also.  The nose is not a painted metal object but rather a plastic radome that likely has the color embedded in it.  My theory is that they leave these unpainted so that you don't get a ragged effect as the paint wears or chips off over time.

It is definitely the first panel of the engine pylon and is indeed left unpainted. Would be interesting to know why.

@757toga from this picture it seems to be riveted.

It's not heated. It's probably made of a material that is difficult to obtain paint adhesion, say titanium or some grade of stainless, or doesn't need paint because it's a corrosion resistant material and they are saving a few ounces, or some other reason known only to insiders.

@JohnK: that's titanium, right. Is it really difficult to be painted? The Blackbird was definitely painted  :)

Titanium requires elaborate processes to get paint to stick, acid etching, sometimes sandblasting.  They may just leave the paint off BECAUSE it's titanium or stainless (more likely) so they can leave it unpainted without worrying about corrosion.

It is also specifically covered during manufacturing: https://www.flickr.com/photos/131621852@N02/33312795343/

Not just the Rolls-Royce XWB, but also the R-R Trent 7000 on the newer A330neo:

LMP 2001, CC BY-SA 4.0 https://creativecommons.org/licenses/by-sa/4.0, via Wikimedia Commons

Airbus made changes to the forward mounting of the engine by incorporating a "cradle" system under that metal part.
The cradle's main function is to reduce the inlet deformation encountered during e.g. take offs.
The specifics are hard to tease out of the patent legalese, but there's mention of impact resistance to that now more forward structural area (which would explain why the cover is now metal—the patent mentions the "Fan Blade Out", and the location of the new system is indeed inline with the trajectory of an ejected blade). Photos after flight testing also show this panel removed, which hints at a post-flight visual inspection of the structural integrity of the new system with respect to the aforementioned inlet deformation (a photo is linked at the end of the answer).
Note that item 31 in the drawing below is optional according to the patents; item 24 (in the first linked patent) not shown below is what you're asking about, but the drawing shows what is now under it. The routing of hydraulics and electrical also goes through the cradle, and there's no mention of an anti-ice system there.
As to why it's not painted, that could be:

If the panel's skin is load bearing, which is likely since the function of the new unit is absorbing the loads that lead to inlet deformation, i.e. under cyclical loads, the paint would crack—similar to this big unpainted joint on the A380 (Q&A); and/or:
Weight and manufacturing cost/time saving as paint for corrosion resistance is not needed for titanium parts (ref: Henriques, Vinicius AR. "Titanium production for aerospace applications." Journal of aerospace technology and management 1.1 (2009): 7-17.), which the A350 makes use of in the pylon and other systems.

Public domain from one of the patents assigned to Airbus

Dussol, Loic, and Frederic Ridray. "Fan cowl support cradle mounted on the attachment pylon and on the air inlet of the nacelle." U.S. Patent No. 8,382,031. 26 Feb. 2013. https://patents.google.com/patent/US8382031B2/en
Roche, Frederic. "Aircraft engine assembly comprising a junction aerodynamic fairing mounted on two separate elements." U.S. Patent No. 8,162,254. 24 Apr. 2012. https://patents.google.com/patent/US8162254B2/en

Photograph: H Gousse/Airbus/PA via theguardian.com; alternate link via aerospace-technology.com
Photo showing the aforementioned panel removal

Consider this a good-enough answer from what is publicly made available by Airbus. It should go without saying that patents don't spill all the beans.

This doesn't explain why the panel needs to be unpainted. Metal can easily be painted without affecting impact resistance. In fact, you want to paint critical metal pieces to minimize possible weakening due to corrosion.

@user71659: If it's subject to concentrated cyclical loads, the paint would crack. The A380 also has unpainted metal joints for that reason (see this older Q&A of mine), but keep your downvote.

Your answer doesn't say anything about concentrated cyclical load, you bold the words "impact resistance". The answer is incomplete, as evidenced by some further explanation you had to give in the comments.

@user71659: "The cradle's main function is to reduce the inlet deformation encountered during e.g. take offs." // The panel's skin would be subject to the same. The question didn't ask why it's not painted; if it had, I would have remembered to make that remark; but instead of waiting for a response, you decided: "Nah, this answer isn't useful one bit" (see the help center, unless they changed it); so as I said, keep the DV.

The cradle does that, but it's not the "forward aerodynamic structure" in the patents. A easy method to prevent loading is to let it float over the rear structure or add compliance in the mounting hardware. This answer lacks an explanation of why the skin/forward aerodynamic structure is loaded (or even a mention that it is loaded), and only points out the cracking problem in the comments.

@user71659: RE "A easy method to prevent loading ...": Unless it's needed in distributing and absorbing the loads... you do realize that patents don't spill all the beans, right? Good day/evening to you; I'm done here.

You figured it out when you wrote the question. It's because the engine nacelles are equipped with anti-icing heaters powered by air from a compressor port, and painting those areas would be counter-productive. Same with the inboard sections of the wings.

@757toga No, I am saying that it has a heater for anti-ice. There appears to be a NACA scoop just forward of that in the nacelle design for the -1000.

Can you update with relevant sources @JuanJimenez? I tried to look up and found what @757toga says is correct. I cannot find any pylon heaters but only nacelle heaters. https://www.smartcockpit.com/docs/a350-900-flight-deck-and-systems-briefing-for-pilots.pdf

You won't get ice accretion on  areas like that unless it's runback ice and cowls are usually evaporative heating to prevent that. The A350 anti-ice system description doesn't mention a heated panel.

My use of terminology was unclear. There are no electric heaters there, it's all heated with hot air from a compressor port. I believe this patent from GE: https://patents.google.com/patent/US5088277A/en explains how the anti-icing system not only heats the ring around the cowling but also the plate in question.

@JuanJimenez But the A350 is powered by RR Trent XWB, not GE engines. I haven't seen this part unpainted on other RR Trent engines, or any GE engines for that matter.

Patents can be licensed so who owns the patent is irrelevant. The reference in the patent is anything that mentions Figure 2 or item 16.

The patent does NOT show the shiny metal plate on the pylon being heated. Fig 2 is a cross-section of the inlet cowl at the 12 o'clock position. I believe the drawing is being mistaken for a drawing of the forward end of the pylon. Accordingly, Item 16 is the outer wall of the inlet cowl, not the shiny plate of interest.


text:
How to properly implement and understand Theodorsen's function?
I'm attempting to implement Theodorsen's lift deficiency function for an airfoil experiencing a harmonic variation in angle of attack due to an oscillating freestream (i.e., not pitch oscillations).  Following Leishman's Helicopter Aerodynamics I have an expression for this (as follows), but I'm unsure how to implement it.
$C_l=2\pi\left[C(k)+i\frac{\omega b}{2v_\infty}\right]\bar{\alpha}e^{i\omega t}$
where $\omega$ is the circular frequency of the AoA oscillation, $\bar{\alpha}$ is the amplitude of the oscillation, $b$ is the semi-chord length, and $C(k)$ is Theodorsen's function, evaluated at a given reduced frequency.  I get my values for this from http://soliton.ae.gatech.edu/labs/windtunl/classes/unstaero/unstaf/theofn.html.  This expression is then plotted against angle of attack, given as $\alpha=\bar{\alpha}sin(\omega t)$.  Using Matlab to plot the real part of this expression, I get the following:

As shown, all I get is a rough circle.  I should be able to plot a hysteresis loop similar to this (from Leishman, Principles of Helicopter Aerodynamics, 2006):
I realize that both plots are for different ranges of angle of attack, but the expression should produce similar results (in terms of trends, appearance) in either case.  Am I missing something on the implementation of this function, or in my understanding of what this function should do?

Could you provide some more details about your implementation like the values for $\omega$, $k$ and the software you're using? I just tested it and get a hysteresis loop like the one in your question. 2. Did you derive the $C_l$ expression yourself? Isn't a $\pi$ missing ($C_l=2\pi\cdot [...]$)?

Ah, you're right.  I copied it incorrectly from the Leishman text I mentioned...editing.  As for the results: I'm using Matlab to plot the real part of the expression for a reduced frequency, k, of 0.1.  Since $k=\omega b/v_\infty$, I find $\omega$ to be 5 rad/s ($v_\infty=25$ ft/s, $b=0.5$ ft).  I use $\bar{\alpha}=8^\circ=0.140$ rad and plot over t=0,3, which should be about 2 periods.  How do you get your results?  I'll put up a plot of what I'm getting too.

The assumption to get the $C_l = ...$ formula is $\alpha(t) = \bar{\alpha}\cdot e^{i \omega t}$. The real part of the angle is $\alpha=\cos{\omega t}$, not the sine.  That should fix your plot. I'll try to post later an answer with some background for readers unfamiliar with Theodorsen.

Oh bother.  Yep, that's it.  Thanks!  I'll pick your answer as soon as it's up.


text:
How does a two-stage supercharger work?
How does a two-stage supercharger like the one found in a Rolls-Royce Merlin work? Does the pilot have any control over it?

Actually yes.  A two stage supercharger used a compressor with two or more compression stages, often with an inter cooler between them, driven by a transmission with different gear ratios to control the compressor speed.  A schematic of this type of supercharger can be seen here on a Rolls Royce Eagle engine.

On the Supermarine Spitfires powered by the larger Griffon engines the supercharger speed had both a LO and HIGH setting and could either be manually controlled by the pilot or automatically controlled.  The HIGH setting was not recommended at lower altitudes to prevent overboosting during operations there.


text:
Do aircraft engines come with electric generators?
For turbojet/fan/prop engines, do they come with an electric generator when delivered to aircraft manufacturers, or it is something that the aircraft manufacturer has to find or make themselves?
I am especially interested in whether GE H-series H85-100 and H85-200 engines come with electric generators?

For turbofan engines, there is usually a very small generator included that powers the engine controls.  If the aircraft manufacturers wants a big generator to power the aircraft (and they pretty much always do), that is furnished by the aircraft manufacturer.  They generally do not make it themselves, they buy it.
I do not know for turboprops.

The two engines cited in the question have no FADEC/EEC so I guess this generator is not present either, EEC is an option it seems. Or is this generator also used for igniters?


text:
Why does air density drop when speed nears the Mach 1?
In many questions and answers about high speed aerodynamics here it is said that as speed approaches the speed of sound, there is also a decrease in air density.
Can someone explain why?.

Can you add a link to at least one such question?

We start with the Laplace equation for the speed of sound: $$a = \sqrt{\frac{\gamma \cdot p}{\rho}}$$ and differentiate and square it: $$a^2 = \frac{\delta p}{\delta\rho}$$
Now we can write: $$\delta p = \delta\rho \cdot a^2$$
Next to be replaced is the pressure differential $\delta p$, using the equation for the conservation of momentum in its differentiated form: $$\delta p = -\rho \cdot v \cdot\delta v$$
$$\rightarrow\:-\frac{\delta v}{v} = \frac{\delta\rho}{\rho} \cdot \left(\frac{a}{v}\right)^2$$
which can be written as $$-\frac{\delta v}{v} \cdot Ma^2 = \frac{\delta\rho}{\rho}$$
Interpretation: At small Mach numbers, changes in speed cause negligible changes in density, but as Mach approaches unity, both are of similar magnitude. With $Ma>>1$, changes in density will become dominant. A speed increase is always coupled to a decrease in density.

wonderful derivation! -NN

A little bit late to the discussion, but I've been trying to figure this out for about a week now. Why do small Mach numbers cause negligible changes in density? Asked differently, what makes this relationship non-linear? Thanks.

@Wyatt Short answer: Physics. Longer answer: An integration over speed is involved to arrive at energy, so energy-related things like dynamic pressure or Mach effects go with the square of it. Mach = 1 is significant because that is the speed at which pressure changes travel in air. If you find this still too simple, pick a good book on molecular dynamics. And read it.

@PeterKämpf oh okay. So it would make sense for dynamic pressure to not scale linearly. Does static pressure also not scale linearly? For me personally it's hard to understand why below Mach 0.3 density doesn't change much. (Also, are you talking about the pressure around shockwaves here? Someone on a different answer said that this answer was talking about shockwaves, so I didn't know if this one was also.)

@Wyatt At low Mach there is too little energy in the kinematics of gasses to affect density much. Not enough force to pull the molecules apart, if that helps. Static pressure is static, so speed has no influence on it. Here it is density: The static pressure is what is needed to keep the column of air above it suspended. Since this column shrinks when you go up, so does static pressure. This answer is not about shockwaves.

@PeterKämpf Ah okay. The part about the molecules not having enough energy to pull each other apart really helped. Thanks


text:
What are the variables of the induced drag formula and where does this force apply?
I want to understand a little bit more the induced drag force, therefore in analyzing the formula:
$$
F_D = C_DA\frac{⍴V^2}{2}
$$
what do the following variables actually mean?
$ F_D $ Is the 3D induced drag. If we take this force as a vector, where should I place it? I've read in another post about the drag center, how can I calculate it if needed?
In addition, I would have to calculate the induced drag force taking only 1 wing's half, should I take the area of the wing's half

You should link the "other post" you read. Otherwise, there is a high probability the answer will be the same and it will stay as blur as it is now for you.

That is not the formula for induced drag, but rather for parasite (pressure+friction) drag. Induced drag is inversely proportional to dynamic pressure. The formula for induced drag is $D_i = \frac{L^2}{\frac{1}{2} \rho V^2 \pi b^2 e}$ where $L$ is lift, $b$ is wing span and $e$ is efficiency factor. Note that lift is constant in straight flight, so it is in practice really inversely proportional to dynamic pressure. Substituting for lift would cancel the dynamic pressure terms, but the inverse proportionality would just hide in $C_L$ variation.

@JanHudec Hi Jan, what does π mean in that formula? Regards, EP.

@ElectricPilot $\pi$ means $\pi$. 3.14159… $\pi$ always means $\pi$.


text:
Why, during a magneto check, does manifold pressure increase as RPM decreases?
When performing a magneto check or exercising the propeller prior to take off (constant speed propeller), you notice that as the rpm drops the manifold pressure rises slightly. Why does the manifold pressure rise?

Welcome to aviation.SE! Does this question help you?

… or this one?

Does this answer your question? Why does manifold pressure increase when you turn on carb heat?

This question isn't asking about Carb Heat. We may well have a duplicate question somewhere, but that isn't it.

I think FreeMan's edit is a good fix.  I agree, this isn't a duplicate.

@RalphJ, the one about carb heat has a better explanation. But if you don't like the fact they have different titles, the first one I linked asks about RPM.

@RyanMortensen, after the edit, it is definitely duplicate of https://aviation.stackexchange.com/q/75395/524

On the intake side, the engine is effectively a vacuum pump; it's sucking in air past a restriction in a duct - the venturi and throttle plate, creating a partial vacuum in the intake passage, and measured as total pressure in inches of mercury (In cars, the MP gauge is labelled "vacuum"; similar, but expressed as a differential between ambient and duct pressure instead.  The problem with car style vacuum gauges is you can't use it to measure horsepower because you don't know the absolute pressure in the intake duct, only the differential, and you'd have to know the actual ambient pressure to work out what is the actual intake duct pressure).
With the restriction being fixed (not moving the throttle), anything that changes the pumping rate (directly tied to piston speed, therefore RPM) affects the amount of suction created between throttle plate and cylinder.  Decrease the pumping rate (or sucking rate you might say), and the vacuum goes down/MP goes up.  And vice versa.
So anything that raises RPM without moving the throttle plate moves MP down a bit because the piston is sucking harder because it's going faster, and anything the reduces RPM without moving the throttle plate moves MP up a bit, because the piston's moving slower.  As you get familiar with this, you learn to drop MP about half an inch below target when following up with an RPM reduction, knowing it will come up as you reduce RPM. And vice versa on power increases.

Think of manifold pressure as being the pressure of the air between the throttle door and the intake valve to the engine cylinder.
Consider that the engine is pulling air through this area.  If you impede that flow by closing the throttle, the pressure decreases.  Why?  The engine is still pulling the air very strongly like a vacuum pump, but the throttle door closing, blocks the flow, so it creates a drop in pressure.  If you open the throttle, it gets out of the way of the airflow and therefore there is a pressure increase because the air is being replaced more quickly/easily as it is being drawn into the engine cylinder.
So, if the engine is creating suction and thus dropping the pressure, then it follows that decreasing engine power via methods other than changes in the throttle setting, would cause an increase in manifold pressure because now, rather than changing the impedance of the airflow vs. the suction of the engine, the amount of suction generated by the engine is what is being reduced.  Reducing the amount of vacuum pressure (suction), leads to an increase in air pressure between the throttle door and the intake valve at any given throttle position.


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How heavy are the Boeing 747 landing gear?
Does anyone know how heavy are the combined landing gear on a Boeing 747?
It would be interesting if someone has also weight statistics per gear (nose gear and the four other main gear).

I don't have those figures, but if it helps, here are the moment changes for gear retraction, i.e. gear down to gear up and a negative moment is a forward change: Nose -167900 lb-in, Body -545600 lb-in, Wing -493900 lb-in. The figures are from Boeing Document No. D04U544-GPR1 for a 747-400BCF.

It could help the answerers to orient better if you can add the reason you need this info. What is the definition of the mass, that you are searching for (hydraulics included or not, brakes, doors, included or not, etc). Rule of thumb is that (for pre-sizing of aircraft) you can take 5-8 percent of the mtow.

@GürkanÇetin: Your percentage is a little high. 3% to 5% is normal, details depending on gear length and maximum sink rate.

It seems I misspoke in my comment in which I gave the moments for 747-400BCF gear retraction. I didn't realize the component weights were further on in the document I referenced. The weights for the BCF are:
body gear 6447 lbs (2924 kg) each
wing gear 6508 lbs (2952 kg) each
nose gear 3157 lbs (1432 kg)
However, @Gurkan's comment is relevant in that you have to decide what all should be considered as part of the gear. So, I put up a PDF of the WEIGHT AND BALANCE CONTROL AND LOADING MANUAL for each of two 747 freighter variants. You can access them at terryliittschwager.com/wbmanuals.php. The most relevant sections are 1-86-041 and 051.

I love that the nose gear of a 747 is considerably heavier than an entire fully loaded Cessna 172.

Is that just the weight of the strut, or a fully assembled landing gear, complete with tires, brakes, downlocks, etc.?


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Can I generate & transmit ACARS message via software?
Is there any software available for generating ACARS message? If yes how to transmit that over RF?.
I want to do that for academic purpose. My settings are GNU radio and HackRF one.

Welcome to [Aviation.se]. Please take the [tour] to help understand how this site is different than your run-of-the-mill discussion forum. Then, if you'll take a look in the [help] under "asking", you'll see that "resource location" questions are explicitly off topic.

For transmitting, you might ask on Amateur Radio Stack Exchange as rules can vary depending on country.

If you are going to generate and transmit them, do you have the appropriate equipment to receive and decode it? Are you taking precautions to avoid transmitting outside of a controlled area (faraday cage)?

You are unlikely to have a permission for sending technical messages over radio channels used by real aircraft.
But if you just want to make your drone to send you ACARS messages over WiFi, there are 144 open source projects currently on GitHub to deal with these messages. Most of them are parsers, not senders, but anyway selecting the best projects and then understanding the code should give enough insights about the message format. Also, parsers can be used for checking that your sender works properly.


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What control surfaces do I need to move to do a roll in a model aircraft?
Figured that this was the better site to ask than drone SE, but if I'm wrong just let me know.
I'm making a spitfire model and was just wondering how do I do a roll? I have elevator, rudder, and two connected ailerons.
What control surfaces do I move to do a roll?

What do you mean, "connected together"? As in, when you try to move the elevator, it moves the rudder and ailerons at the same time? Because such an airplane would barely be controllable in straight-and-level flight, much less being able to do any kind of aerobatics.

@HiddenWindshield, sorry, only the ailerons are connected so if one is up both are up. rudder and elevator move independently

Ah, ok. That makes it easy to answer.

Related: How is ruder used in an aileron roll?

Might also want to go back and double check the building instructions book.  If your ailerons both move up together, something is hooked up wrong.

@ZeissIkon, here is the build vid and they fly it just fine with ailerons both hooked up together and you can see they manage to roll around 47:00.

@Ceramicmrno0b Yes, ailerons are "hooked together" -- usually they run from a single servo (though larger models may use one servo in each wing).  They're set up so one goes up when the other goes down, however -- commonly managed by having a horn on the bottom of each aileron hooked via pushrod or pushrods and bellcrank to the same servo arm, so when the servo pushes one (up) it pulls the other (down).  I set up my first one in 1986, and I looked at them for about fifteen years before that, before I could afford one.

The ailerons should be connected so that they move opposite each other. When one aileron moves up, the other one must move down, and vice versa. In fact, in full-size aircraft, the ailerons are connected so that it's actually impossible to move them in the same direction*. So, to answer your question, to roll to the right, the right aileron must move up and the left must move down.
*Well, certain airplanes have "drooping ailerons": when the flaps are deployed, it causes both ailerons to tilt downward slightly. But this is about increasing lift at low airspeeds, it doesn't affect how the ailerons control.

To perform a roll maneuver in flight, there are essentially three choices.
The easiest is an aileron roll.  For this, a small reserve of airspeed is needed above stall; the nose is raised and elevator neutralized, then full (or for some models, partial) aileron is applied in the direction of the desired roll.  Elevator and rudder are kept neutral as the aircraft rolls, and if the roll rate is correct, the nose will have dropped about as far below horizon as it was lifted before the maneuver at the time the wings come level.  Roll is then stopped with reversed aileron (not much is needed with a stable model), and the nose returned to level flight at nearly the same speed as entry.  A variant of this, the barrel roll, carries up elevator through the entire maneuver, thus keeping positive G loading on the airframe.
Next is the snap roll.  This is a stalled maneuver, essentially a spin in a horizontal direction rather than vertically descending.  At 2x stall speed, the nose is raised sharply with rudder is applied in the direction of the desired spin.  The wing will undergo accelerated stall at about 1.5G, the rudder input will cause the aircraft to autorotate.  Rudder is reversed briefly to stop the roll when the wings approach level, and the elevator released to unstall the wing.
Most complex, and hardest to perform well, is a slow roll.  This requires a similar reserve of airspeed to the aileron roll, but the nose is kept on the horizon.  Aileron is used to roll the aircraft at significantly less than maximum roll rate, while rudder and elevator are coordinated to keep the nose level throughout the maneuver.  Opposite aileron halts the roll (with elevator and rudder back to neutral) when the wings are level and aircraft upright once again.  In order to keep the nose level, progressively increasing, then decreasing rudder inputs (toward the high wing), combined with progressively increasing and decreasing "down" elevator input as the aircraft passes through inverted flight, are required.  When done well, the aircraft will appear to roll around an invisible string passing from the nose through the tail.


text:
Pressure distribution on Aircraft wing
While conducting a structural analysis FEA for an aircraft wing, I had to import the CFD pressures acting on the wing, lets say at an A.o.A = 10 deg, at 80 m/s and at  sea level, and say the atmospheric pressure is 1 atm. Should the imported pressures from CFD analysis (on the top surface and bottom surface of the wing) be the absolute static pressures or the net pressures? (Assuming the wing surfaces have no slip condition).
If I use the absolute pressures, then the top surface would be experiencing a positive pressure meaning that the pressure is acting onto the top surface (causing it to shrink), and if I use net pressure then that would be negative meaning that the pressure is acting out of the top surface (causing it to expand).
Which one is true? I think that absolute pressures should be used because if, for example, we want to know the structural behavior of the wing top/bottom surface under 1 atm only (assuming wing is symmetric and at an A.o.A = 0 deg), then the net pressures would be zero and we wouldn't have any forces acting on the top or bottom surface of the wing.
Also, does the wing's top surface, in reality when it is flying, deform out (i.e. expands) or deforms in (i.e. shrink)? I think since the absolute pressure is still positive so it must deform in, but some sources say that it instead deforms out. (Assume a static structural condition). A such source I am attaching in the picture.

I adjusted the wording a bit to try to make the question a little more grammatically correct. Also, it appears that the picture relates to your add-on question, so I moved it to the end.

Wings are hollow and open to the atmosphere, so ambient pressure acts on both sides of any surface and nets to zero.

That just adds confusion.  Yes, if there is no in or out flow inside the wing we can say it has atmospheric pressure inside. SO. . .that upper skin has less pressure above and more below, so the inner pressure Pushes the skin up which then pulls up on the ribs and spar.   BUT. . . the lower skin also has more pressure below than above it and pushes the ribs and spar up.
Wings are hollow, but don't need to be, so it's better to leave that out for a basic unde3rstanding.

When applying a FEA loadcase, you should always keep in mind the complete picture of which forces are applied on any surface, and in what situation you consider the wing "undeformed".
If you start out with a solid wing in the vacuum of outer space, and descend into the atmosphere, then indeed the wing will compress under a hydrostatic pressure. But this is an unlikely scenario.
A much more likely scenario is that you want to compare the deformation from standing still to flying. The initial situation is already in the atmosphere, and you would typically say this is the undeformed situation. When you want to calculate the deformation when flying, you would only apply the pressure difference. This is the most common way of doing FEA analysis.
If you're interested, the following explains what happens if you do apply atmospheric pressure. Under the assumption of linearity, we're allowed to split the loadcase into differential pressure and atmospheric pressure. So the question is really what happens if you apply atmospheric pressure. The answer is: very little. Remember that atmospheric pressure also acts on any surface on the inside of the wing. The net result is that the entire wing is under hydrostatic pressure. This adds a measly 0.1MPa to the stress of the wing. Furthermore, most failure criteria for structural materials explicitly remove the hydrostatic stress. For example, in the Von Mises stress, hydrostatic pressure doesn't show up at all. So in effect, very little happens and only pressure differentials are applied in FEA.

For a wing having, for example, vaccum inside of it, then according to what you said, the absolute pressures should be imported, right?

Exactly. Basically, using net pressures is a very convenient simplification since we typically do not care about the hydrostatic stress. You could even apply a -1atm net pressure instead of 0 absolute pressure.

TO answer the question stated.
TO BE PERFECTLY CLEAR:
ALL pressures around a wing are INWARD toward the surface.
In your terms, the upper wing skin is not 'bulging' outward.  It is being pressed inward by something a little less than the ambient atmospheric pressure that is far from the wing; or if the wing was stationary.
.
All surfaces EXPERIENCE "positive pressure".
Even a stalled wing.
In normal flight, wings do not cavitate.


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Electric Airplane - Hybrid / dual type engines how would that work?
If you have an airplane with electric propellers for take off and landing and you have a turbofan/jet to reach higher speeds for cruise.
For example, electric propellers can go to 250mph and turbofan to 550mph

Do you switch off the electric propellers or leave them on ?
Do they work in conjunction ?
What is the effect on the propellers when the turbofan reaches 550mph ?
Is the thrust added if both engines are working ?

imho, what could make sense is the opposite: jet for takeoff (high thrust) and electric for cruise (moderate thrust), but that electric power has to come from somewhere and with the current technology we are nowhere near to useful.

Have you actually checked if one set of props won't work for the whole flight?  As was discussed by several people in your previous question on this subject, a well designed ducted fan might handle both sea-level take off and high speed cruise at an appropriate altitude.  Modern turbofans handle both duties today, your only difference is electric power.

After thinking it over, based on all responses (thank you all), what i want is a normal turbofan with the front fan being able to start on electricity and once up in air switch on the noisy turbofan core combustion which then can drive the front fan as well.
Again i understand it is counter productive not to use core thrust during take-off however my main objective is silent take-off and not noisy take-off. Some time economics have to suffer for comfort of people living near airfields.

@Arturo First of all, electric motors aren't silent. Second, much of the noise is from air flow and spinning parts, not necessarily the combustion process itself. This would still happen with your proposed electric engine for the same thrust rating. Third, if you don't like the sound of jet engines, don't move next to an airport. That's a much more simple solution that spending billions of dollars in design, manufacturing, and maintenance costs while reducing safety.

The B-36 Peacemaker had 6 radial engines, driving 6 propellers, AND 4 jet engines in 2 nacelles.  The jet engines were used for takeoff and for "dash" over a target.  The jets were turned off during cruise because they used considerably more fuel than the piston engines.
As such, they HAVE made propeller/jet hybrid aircraft in the past, though not electric.
To answer your questions:

You probably want to feather the propellers and kill the electric motors.  If the props can only drive you to 250 MPH, leaving them windmilling in the slipstream when the jets are running will add drag, which will only serve to hurt your cruise speed and/or increase your fuel consumption.
They only work in conjunction as speed BELOW what your props can drive (eg 250 MPH, in your example).  Beyond that, if it's speed you're after, you're better off without the props.
At speeds above what the props can deliver, they're essentially small windmills.  And not very efficient ones at that.
See 2.

Now, what WOULD be helpful as a "hybrid" aircraft would be a gasoline engine, turning a prop, with an electric motor added between the engine and the prop.  The electric motor could supply extra power during takeoff and function as a generator/dive brake on the prop during descent.  In the event the gasoline engine failed, the prop/electric motor assembly could be declutched from the gasoline engine, providing you with temporary power to maneuver around and land safely.  Gasoline engines in aircraft tend to be very reliable, but when they DO fail during take-off or landing, the most vulnerable parts of the flight, the results tend to be catastrophic.  As such, the gasoline/electric hybrid would be of no use during cruise but it MIGHT improve the safety factor during the most vulnerable parts of the flight.

How much drag produces a feathered propeller? Thanks.

Such a hybrid config would be an interesting option for the V22 Osprey - if one engine fails, switch the electric motor on the other side to generator mode. This eliminates the mechanical cross-connect which is currently needed to land after a single engine failure.

@MSalters -- what would be even more interesting is if there were just electric motors on the wingtip nacelles and some kind of "inboard" motor somewhere in the fuselage.  Something like that might make a smaller, lighter version of such an aircraft affordable by "mere mortals."  Like me :-)

@Urquiola for an ATR-72 size/mission aircraft, I found that feathered, locked propellers (around 13-foot diameter) only added about 10-12 drag counts at Mach 0.45, 20 kft

A hybrid just does not make sense on a plane for the same reason that a turboprops make sense on a plane and turboshafts do not for a car. Cars have rapidly varying load, planes do not. Also planes do not brake in the air (often), so regenerative brakes would be worthless. Overall the electric motor in a hybrid car is in effect used to smooth out the load on the internal combustion engine, and allow it to run at its most efficient rpm. In a turboprop, the variable pitch does the same thing, but much better.

I guess there's no current experimental evidence to answer the question about an airplane with an hybrid engine and an added jet engine, but there are some publications about hybrid airplanes, such as: 'A simplified method to calculate the fuel burn of a hybrid electric airplane', R Jagannath et al, in 50th AIAA/ASME/SAE meeting, Propulsion and Energy forum, 2014


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What would be the process to approve a minimal, standardized flight recorder for commercial balloons?
According to this article about the recent balloon event, the NSTB will try to interrogate personal electronic devices for any related data. Since some of these mentioned in the briefing do not contain cameras, they may look for accelerometer, gyro, and altimeter data that may have been captured automatically. Chips for these are commonly found in cell phones, tablets and other personal monitoring devices.
Standardization, performance and reliability are only some of the things that a NTSB-recognized voluntary flight recording device would need. Is there any mechanism or regulatory pathway for a standardized yet voluntary flight recorder for balloons, or would it have to be all-or-nothing - required, regulated, and therefore in the end substantially more expensive?
According to this recent WSJ article:

More than two years ago, the NTSB urged tighter regulation of balloons carrying passengers. Without such changes, the safety board said in a April 7, 2014, letter, “the potential for a high number of fatalities in a single air tour balloon accident is of particular concern.”

Currently, passenger balloons do not file flight plans (see this question and associated answers), and while transponders for balloons may exist they are not required, nor is any passive reflection enhancement for radar.

The "standardized" part is the hard part. Even required CVR's and FDR's are not "standardized" in the terms of data collection. The type of data that is recorded is mandated, but not the method or format. There are products on the market like the Stratus 2s that provide FDR-like logging in a relatively affordable package.

@RonBeyer do FDR's have standardized performance requirements - resistance to extreme temperatures and pressures, automatic submerged "pings" for example? I didn't specify standardization of design.

Yes, I can't find an online version of it, but the requirements are called out in FAA TSO-C123a.

The other problem is if you don't make it mandatory, nobody is going to use it. Anything related to an aircraft is expensive. In reality, for a balloon all you probably could record is altitude and position. Given todays devices like cell phones, a simple app could be a pretty effective balloon FDR, even recording to the cloud since they are probably within range of cell towers, and its not a lot of data...

@RonBeyer regulations vs guidelines, pressure from customers and insurers may all have a role here as all of them do in other forms of aviation. I'm asking here about a potential process for standardizing aspects of a data logger, which will probably end up being somewhat distinct from a phone. Just one example: an app sits behind a password and so may not be recoverable - if as in this case - it needs to be easily, reliably, and without advance warning interrogated by a third party at a significantly later time. Phones are usually designed to prevent exactly that thing from happening.

As Ron mentioned, if you want to produce a "standardized" voice recorder for balloons you'd be complying with FAA Technical Standard Order (TSO) C123 (currently revision C).
Along the same lines if you wanted to make a "standardized" flight data recorder it would need to comply with TSO C124 (and you would have to figure out what data would be useful to record, and how to get that data to the recorder).
If we're not sticking with an established actual standard then the next best thing are the personal portable electronic devices used in the flight - particularly if the balloon operators are using something like Foreflight, Garmin Pilot, WingX, etc. on a tablet. The NTSB lab has a good amount of experience in recovering useful data from these devices, and they can be almost as useful as an actual flight data recorder. Combined with an onboard camera (say a GoPro) capturing audio/video of the flight you can make an excellent reconstruction of events (and since many balloon operators offer their customers a flight video there's a good chance the cameras are already installed...)

It's worth noting however that none of these devices improves the safety of a given flight: CVRs, FDRs and even cockpit video are forensic tools used after a crash or incident to help us understand what happened, but their value is after an incident, and thus usually after loss of life.
The other NTSB recommendations (including carrying transponders) are aimed at actively improving the safety of individual flights, and may prevent incidents.


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Why is the top left corner cut off on the cg location envelope for small airplanes?
Why does the PA-28 C.G. envelope have the top left corner cut off rather than allowing higher weights at a forward C.G. like it does at the aft C.G.?

(source)

It isn't just small airplanes, I've seen lots of business jets that look the same.

The 727, 747, and 767 also have such an envelope.

Please attribute the image with the source.

Possible duplicate of How are the limits of the center of gravity chart established?

With "top left corner" you mean the combination of a heavy airplane and a forward cg location.
This is to limit maximum stick forces. Manoeuvring (= flight at a specified load factor ≠ 1)  needs force proportional to the distance between the cg and the neutral point ("static margin") and the mass of the airplane. There are several situations in which certification requires not to exceed specific maximum forces. For example, FAR Part 23.145 says:

(b) Unless otherwise required, it must be possible to carry out the
  following maneuvers without requiring the application of single-handed
  control forces exceeding those specified in §23.143(c). The trimming
  controls must not be adjusted during the maneuvers:

[...]

(c) At speeds above VMO/MMO, and up to the maximum speed shown under
  §23.251, a maneuvering capability of 1.5 g must be demonstrated to
  provide a margin to recover from upset or inadvertent speed increase.

Another would be out of trim situations as those in Part 23.255:

(f) In the out-of-trim condition specified in paragraph (a) of this
  section, it must be possible from an overspeed condition at VDF/MDF to
  produce at least 1.5 g for recovery by applying not more than 125
  pounds of longitudinal control force using either the primary
  longitudinal control alone or the primary longitudinal control and the
  longitudinal trim system.

Is Vdf the demonstrated diving speed? Also, where may one find such information if it is not in the POH nor in the TCDS?

@Pugz: Yes, VDF is the demonstrated dive speed, so Mach effects can be included to lower the dive speed from the usual VD value. For the PA-28 the regular VD applies (VDF/MDF are used for jets only). Part 23.335 defines those speeds (but not VDF explicitly).

Very cool, thanks!